Well the test results are in. My runner's iron was excellent (ferritin 95, hemoglobin 15.9), testosterone was excellent (505), but thyroid was terrible (TSH 4.8) meaning he has "sub-clinical hypothyroidism" which explains his terrible running the past year. As posted previously by another guy familiar with this condition, runners run best with a TSH between 1.2 and 1.5. This is a terrible break for a 20 year old.
He has 2 options going forward and I have decided to not give him a recommendation because this is a medical issue far more important than competitive running which we are just doing for fun and this decision should between him, his family and his doctor.
1) Do nothing for now. The pros are he won't have to go on long term medication at such a young age. He won't have the side effects of the drug Synthroid (Levothyroxine). His thyroid will decline at a slower rate than if on the medication. He is not at a clinical level yet (TSH 5-7 depending on the source) and may not be for a few years. He can continue to run for fitness. The cons are his competitive running career will be over (no point in competing when at age 20 you are much slower than you used to be and not matter how well you train, you will get a little worse every year). He will feel tired when he runs. Although he doesn't feel fatigued in daily activities, eventually he will. He will continue to be very sensitive to cool temperatures and it will worsen with time. He doesn't have any muscle soreness or joint soreness now but he will eventually. He doesn't have any "foggy head" symptoms but will eventually. His LDL "bad" cholesterol levels will gradually rise and he will eventually he will have serious heart issues.
2) Start taking the drugs. The pros are he won't have any of the effects of hypothyroidism (fatigue, cold sensitivity, foggy head, rising bad cholesterol, muscle soreness/joint soreness and eventually heart issues). He can resume competing and will be back to his prior performance level in a couple of months and can continue to improve for many years to come. The cons are he will be only 20 years old and on long term medication. He will suffer side effects and as anyone who is familiar with drugs, it will eventually lead to having to go on more and more drugs as we have all observed in the elderly once they start taking drugs. His thyroid will decline faster, meaning there is no turning back, once on the drug, you are on it for life. It is hard to get the dosage correct and it has to be tweaked several times in the first 2 years to get it right and if the dose is too high or too low you will have problems.
It is a shame this happened to the kid and I will support whichever way he decides.
I have to admit I was surprised how only a few posters to this thread recognized that there was an obvious physical issue and the rest thought it was a training issue or even a psychological "head case" issue. It shows that one can and should learn a lot by reading about and listening to successful coaches and from one's own running experience and that of their peers. However, that is not enough, in addition to that critical knowledge, you need to be down in the trenches, i.e. coaching a large number of people over several years to fully understand the whole thing.